Suppliers of electrical energy experience, on a daily basis, an overall demand for electrical energy that has peak periods and off-peak periods. Typically, in a domestic situation, there would be two peak periods each day. The first is in the morning corresponding to people arising, taking a shower or bath, using stoves and kettles in order to have breakfast and possibly turning on electrical heaters in cold weather, prior to going to work. The other peak period takes place in the evening when people return from work, use cooking appliances in order to prepare the evening meal, take a shower or bath and possibly use electrical heaters or air conditioners, as the case may be. In addition, there may be the use at these times of other appliances such as washing machines, tumble driers and dishwashers, all which consume considerable electrical energy.
Clearly, the infrastructure of an electrical energy supply system must be able to cope with the peak period demand and, accordingly, at off-peak periods, there is generally surplus capacity.
Electrical storage type of water heaters contribute significantly to peak loads as their thermostats switch on soon after a supply of hot water has been withdrawn from a hot water storage tank forming part of the water heater. Numerous different systems and proposals have been put forward in order to try and control the times at which water heaters draw electrical energy from the electrical supply system and many are in practical use.
One approach has been for a central control facility to communicate with switching arrangements associated with remote water heaters by way of signals transmitted over the electricity supply grid; over telephone lines; or by way of wireless communication. These arrangements are expensive; require ongoing management; and may not be appropriate to less sophisticated installations.
Another approach has been to use real-time time switches for restricting water heaters to operation during off-peak times. Whilst, in theory, this arrangement operates effectively, it has certain drawbacks including the fact that real-time timers are generally costly and generally do not keep the time of day indefinitely, needing to be reset periodically, particularly if there has been an interruption in the supply of electrical energy. Timers with a so-called reserve or back-up to energize them during supply interruptions so that they maintain the correct time are even more costly.
Accordingly, whilst enjoying certain popularity, applicant believes that the use of such real-time timers is not sufficiently widespread to assist the suppliers of electrical energy to any substantial extent, at least in many different electrical supply regions. Also, this system is inappropriate in unsophisticated systems because of the necessity that the electrical energy drawn during peak periods be distinguished by a real-time clock from electrical energy drawn during off-peak periods or, a real time based formula needs to be actively applied by somewhat sophisticated metering equipment.
Other rather sophisticated computer controlled techniques have also been developed in an attempt to monitor, predict, and control the electrical energy consumed, for example, by a household or other consumer. U.S. Pat. No. 6,208,806 to Langford is an example of such a control system. Numerous other computer based systems have been proposed. All of these are complicated, expensive, and inappropriate to numerous unsophisticated electrical supply grids.
As regards unsophisticated electrical supply installations, it is also often a problem that one particular electrical circuit has insufficient capacity to operate two or more appliances simultaneously and there is a danger that the circuit becomes overloaded.